Diets high in saturated fats increase low density lipoproteins (LDL), which in turn causes the deposition of cholesterol on blood vessels, a pre-condition closely correlated with atherosclerosis and coronary heart disease (Conner et al., Coronary Heart Disease: Prevention, Complications, and Treatment, J. B. Lippincott, Philadelphia, 1984 pp. 43-64,). By contrast, diets high in monounsaturated fats have been shown to reduce heart disease. Oleic acid, the only monounsaturated fat in most edible vegetable oils, lowers LDL as effectively as linoleic acid, but does not affect high density lipoproteins (HDL) levels (Mensink et al. (1989) New England J. Med., 321:436-441). Furthermore, diets high in monounsaturated fats are also correlated with reduced systolic blood pressure (Williams et al. (1987) J. Am. Med. Assoc., 257:3251-3256, 1987).
In light of the effect of fatty acids on diet and health, attempts have been made to alter the fatty acid profile of plants used for edible and industrial purposes. However, conventional methods of altering plants to improve the fatty acid profile rely on mutagenesis (e.g., chemical, radiation, etc.) and/or breeding and are time-consuming, laborious and do not specifically target selected genes. See, e.g., U.S. Pat. No. 5,861,187.
Recently, engineered DNA-binding domains such as meganuclease DNA-binding domains and zinc fingers proteins (ZFPs) have been used advantageously to selectively modulate gene expression and for targeted alteration of gene sequences in plants (see, e.g., U.S. Pat. Nos. 7,262,054, 7,235,354, 7,220,719, 7,001,768, and 6,534,261; U.S. Patent Publication Nos. 2008/0182332 and U.S. Ser. No. 12/284,888). Zinc finger proteins (ZFPs) are proteins that bind to DNA, RNA and/or protein, in a sequence-specific manner, by virtue of a metal stabilized domain known as a zinc finger.
See, for example, Miller et al. (1985) EMBO J. 4:1609-1614; Rhodes et al. (1993) Sci. Amer. 268(2):56-65; and Klug (1999) J. Mol. Biol. 293:215-218. ZFPs are commonly found in transcription factors, and to date, over 10,000 zinc finger sequences have been identified in several thousand known or putative transcription factors.
DNA-binding domains can also be used with nuclease domains to make engineered nucleases. For example, the DNA-binding domain of a homing endonuclease can be altered to generate novel homing endonucleases. Similarly, zinc finger domains have also been combined with nuclease cleavage domains to produce zinc finger nucleases (ZFNs) for specific targeting of a double-stranded break to the region of a genome where modification (e.g., deletion, mutation, homologous recombination, or insertion of an exogenous sequence) is desired (see, e.g., U.S. Patent Application Publication Nos. 2007/0134796; 2005/0064474; 2008/0182332). Engineered ZFPs greatly facilitate the insertion of exogenous sequences or modification of endogenous sequences at specific target sites in plants and provide for targeted alteration of plant genomes with greater efficiencies than conventional methods (see, e.g., U.S. Pat. Nos. 7,262,054, 7,235,354, 7,220,719, 7,001,768, and 6,534,261).
Nonetheless, there remains a need for compositions and methods for targeted alteration of genes involved in fatty acid synthesis in order to produce plants and plant products (e.g., plant oils) having selected fatty acids. By producing plant varieties with reduced levels of individual and total saturated fats in the seed oil, oil-based food products which contain less saturated fats can be produced. Such products will benefit public health by reducing the incidence of atherosclerosis and coronary heart disease.